1. Field of the Invention
The present invention relates to a semiconductor device and a method of controlling the same, and more particularly to a semiconductor device including internal voltage generating circuits that generate an internal voltage and a method of controlling the same.
2. Description of Related Art
Semiconductor devices such as a DRAM (dynamic random access memory) may include a circuit block that operates on an internal voltage different from an external voltage supplied from outside. Such a semiconductor device includes an internal voltage generating circuit that generates the internal voltage based on the external voltage supplied to the semiconductor device. The internal voltage generating circuit supplies the internal voltage to load circuits in the semiconductor device (see Japanese Patent Application Laid-Open Nos. H9-320268 and H11-25673).
In Japanese Patent Application Laid-Open No. H9-320268, a semiconductor device includes a plurality of internal voltage generating circuits connected to a power supply line in parallel. The internal voltage generating circuits start operation in response to a drop in the internal voltage. The operation timing is thus asynchronous to an operation timing of other circuit blocks. Consequently, the other circuit blocks may be affected by asynchronous noise caused by the operation of the internal voltage generation circuits. To solve such a problem, Japanese Patent Application Laid-Open No. H11-25673 describes a semiconductor device including internal voltage generating circuits to produce less noise.
Studies made by the inventors have shown, however, that noise occurring from an internal voltage generating circuit can affect not only circuit blocks (first load circuits) using the internal voltage, but also circuit blocks (second load circuits) using a voltage different from the internal voltage. The noise occurring from an internal voltage generating circuit may propagate toward the second load circuits through various channels such as the semiconductor substrate itself, a ground line supplying a ground potential, and a first power supply line supplying a power source to the internal voltage generating circuit or the second load circuits. It is therefore considered to be desirable that internal voltage generating circuits be controlled in consideration of the operation timing of circuit blocks using voltage other than the internal voltage.